1. Field of the Invention
The present general inventive concept relates to an electrophotographic photoreceptor and an electrophotographic imaging apparatus employing the same, and more particularly, to an electrophotographic photoreceptor having excellent stability in terms of electrical properties and interlayer adhesion strength and an electrophotographic imaging apparatus employing the same.
2. Description of the Related Art
Electrophotographic devices such as laser printers, photocopiers, facsimile machines, CRT printers, liquid crystal printers, LED printers, plotters, and the like include an electrophotographic photoreceptor including a photosensitive layer formed on an electrically conductive substrate. The electrophotographic photoreceptor can be in a form of a plate, a disk, a sheet, a belt, a drum, or the like and forms an image as follows. First, a surface of the photosensitive layer is uniformly and electrostatically charged, and then the charged surface is exposed to a pattern of light, thus forming the image. The light exposure selectively dissipates the charge in the exposed regions where the light strikes the surface, thereby forming a pattern of charged and uncharged regions, which is referred to as a latent image. Then, a wet or dry toner is provided in a vicinity of the latent image, and toner droplets or particles collect in either the charged or uncharged regions to form a toner image on the surface of the photosensitive layer. The resulting toner image may be transferred to a suitable final or intermediate receiving surface, such as paper, or the photosensitive layer may function as a final receptor for receiving the image.
Electrophotographic photoreceptors can be categorized into a negative charge type electrophotographic photoreceptor and a positive charge type electrophotographic photoreceptor according to a charging method. Currently, the negative charge type electrophotographic photoreceptor in which a surface of the electrophotographic photoreceptor is negatively charged and exposed to light is widely used. However, due to disadvantages such as ozone generation caused by negatively charging the electrophotographic photoreceptor, limitations in terms of resolution improvement, and the like, research into a positive charge type electrophotographic photoreceptor in which a surface of the electrophotographic photoreceptor is positively charged and exposed to light has recently been actively conducted.
In addition, electrophotographic photoreceptors can be generally categorized into two types. The first is a laminated-type electrophotographic photoreceptor having a two-layered photosensitive layer including a charge generating layer including a binder resin and a charge generating material (CGM), and a charge transporting layer including a binder resin and a charge transporting material (usually, a hole transporting material (HTM)). The laminated-type electrophotographic photoreceptor may have two configurations, that is, a structure in which the charge generating layer and the charge transporting layer are sequentially formed on an electrically conductive substrate, and a structure in which the charge transporting layer and the charge generating layer are sequentially formed on an electrically conductive substrate. In general, the laminated-type electrophotographic photoreceptor is used in the fabrication of a negative (−) charge type electrophotographic photoreceptor. The other type is a single layered-type electrophotographic photoreceptor in which a binder resin, a CGM, an HTM, and an electron transporting material (ETM) are included in a single layered photosensitive layer. In general, the single layered-type electrophotographic photoreceptor is used in fabrication of a positive (+) charge type electrophotographic photoreceptor.
In general, an undercoat layer is formed between the electrically conductive substrate and the photosensitive layer. The undercoat layer improves imaging properties by preventing charges from being injected into the photosensitive layer from the electrically conductive substrate, covers surface defects of the electrically conductive substrate, improves adhesion between the electrically conductive substrate and the photosensitive layer, and prevents dielectric breakdown of the photosensitive layer. Conventionally, alumite, i.e., aluminum oxides, is widely used in the formation of the undercoat layer. However, in order to reduce costs, an undercoat layer formed by coating a coating dispersion to form an undercoat layer in which inorganic particles are dispersed in a binder resin solution on an electrically conductive substrate has recently been widely used.
A binder resin of the undercoat layer may be divided into a thermosetting resin and a thermoplastic resin. When a thermoplastic resin is used, a process of drying and cooling the undercoat layer after a coating process is not required. In addition, a shelf life of a coating dispersion to form an undercoat layer becomes longer. Accordingly, using a thermoplastic resin as a binder resin for the undercoat layer is economical. An alcohol-soluble nylon resin is widely used as a thermoplastic resin, taking into account suitable properties thereof of adhesion to an electrically conductive substrate, a coating property and an electrical barrier property. However, the alcohol-soluble nylon resin generally has high absorptivity, and electrical properties and imaging properties of the electrophotographic photoreceptor are highly environmentally dependent. To improve a resistance of the undercoat layer in low temperature and low humidity conditions, inorganic particles such as metal oxide particles, or the like, in particular, titanium dioxide particles are used. Such titanium dioxide having an average primary particle diameter of about 30 to 50 nm is widely used, taking into consideration dispersion stability of a coating dispersion and resistivity of a produced undercoat layer.
However, when the undercoat layer is formed only of a binder resin and inorganic particles, adhesion between the electrically conductive substrate and the photosensitive layer, between the electrically conductive substrate and the charge generating layer, and between the charge generating layer and the charge transporting layer deteriorates. Thus, the photosensitive layer, the charge generating layer and the charge transporting layer can be easily damaged by even small impacts, or in severe cases, the electrically conductive substrate and the photosensitive layer, the electrically conductive substrate and the charge generating layer, and the charge generating layer and the charge transporting layer may be detached from each other.
To address these adhesion reduction problems, Japanese Patent Laid-Open Publication No. 2005-227789 discloses a method of improving adhesion by adding a titanium-containing alcohol-soluble chelate compound to a coating dispersion to form an undercoat layer to be cross-linked with a binder resin of a charge generating layer and a charge transporting layer.
However, when the titanium-containing alcohol-soluble chelate compound is added to the coating dispersion to form an undercoat layer, precipitation is easily generated or the dispersibility of the dispersion deteriorates, thus reducing the storage stability of the coating dispersion, and discoloration occurs easily with storage time. When a photoreceptor is prepared using such a discolored coating dispersion, electrical properties of the photoreceptor also deteriorate easily.